The present invention relates to angular and linear displacement and position measurement. More specifically it relates to a differential inductive transducer that translates motion directly into a digital output with a high degree of resolution and low noise.
Angular displacement transducers are widely used in gyros and accelerometers. One problem of such devices is interfacing the transducer with a microprocessor that performs guidance and navigation functions. For servoed rate-integrating instruments this interfacing is presently performed by costly digitized servo electronics. In mechanically simpler and less expensive spring-restrained instruments the interface problem is more difficult since the output of these devices is usually an analog carrier-modulated sine wave.
A common electromechanical device is an inductive displacement transducer. In its typical configuration, either in the rotary or linear form, very small changes in position are sensed by means of variable electrical coupling between a rotor element and a stator element. In one such device one of the transducer elements is supplied with an alternating current (AC) electrical signal, and an Ac electrical signal is generated across the other element. The amplitude of the signal is a function of the relative position of the rotor with respect to the stator. In another such device, the phase difference between the two AC signals is measured rather than the amplitude.
While such devices are in wide use, they produce an analog output which must interface with a digital processor. Numerous difficulties in this interfacing reduce the accuracy of the digital representation of the displacement. The resulting AC signal is low-amplitude and subject to noise thus requiring extensive shielding, amplification, buffering, demodulation, filtering and conversion from analog to digital form. This electronic processing must normally be performed by discrete circuitry located outside the instrument. Further, to provide an acceptable resolution, typically 1 part in 10.sup.4 to 10.sup.5, it is necessary to employ a relatively high precision, high-cost, analog-to-digital converter with a wide dynamic range. Yet another problem is that calibration and temperature and scale-factor compensation has to be provided by complex, peripheral equipment and usually necessitates manual measurements and settings. The requirement for such additional circuitry increases system cost, weight and size while reducing system reliability.
It is therefore a principal object of this invention to provide a differential displacement transducer that translates displacement, whether angular or linear, directly into a digitized output.
Another principal object is to provide such a transducer that is characterized by a high degree of resolution and low noise over a wide dynamic range.
Another object is to provide a transducer with the foregoing advantages that is readily adapted to automatic compensation for temperature and scale-factor variations.
A further object is to provide a transducer with the foregoing advantages that is compact and can be housed as a unit with other components of the measuring instrument.
Yet another object is to provide a transducer with the foregoing advantages that has a competitive cost of manufacture, particularly one which utilizes low cost, monolithic electronic components.